MODIFICATION OF HOST RESPONSES TO BACTERIAL ENDOTOXINS. I. SPECIFICITY OF PYROGENIC TOLERANCE AND THE ROLE OF HYPERSENSITIVITY IN PYROGENICITY, LETHALITY, AND SKIN REACTIVITY

Evidence is presented suggesting that the apparent non-specificity of pyrogenic tolerance observed with Gram-negative bacterial endotoxins is due to related antigenic determinants associated with the macromolecular toxins. This is based on results obtained in rabbits from pyrogenic cross-tolerance tests with selected endotoxins. In these tests, purified endotoxins from Escherichia coli (COO8) and Chromobacterium violaceum (CV) gave results one might expect with non-reciprocal cross-reacting antigens in classical immune systems. Additional evidence for an immune mechanism in tolerance is suggested by the highly significant anamnestic response observed. Lipid A, a toxic derivative of the purified COO8 endotoxin, failed to induce pyrogenic tolerance against the parent toxin. These results are explained by assuming that endotoxins have two interdependent activities associated with different portions of the macromolecule; one is assumed to be responsible for the primary toxicity, and the other is involved in secondary toxicity. The latter is dependent on the hypersensitive state of the host. Additional evidence for the role of hypersensitivity in secondary toxicity is based on the observation that adult rabbits are highly sensitive to the pyrogenic, lethal, and skin-reacting activities of endotoxin in contrast to young animals which are more resistant to all of these attributes of toxicity. In adults, the host responses to pyrogenicity, lethality, and skin reactivity could be partially inhibited by the early exposure of the animals to massive doses of endotoxin equivalent to a LD₅₀. The pyrogenic tolerance shown in these animals was specific indicating that the inhibition of the hypersusceptibility to endotoxin involved an immunological mechanism. A mechanism of endotoxin tolerance is proposed and discussed based on the induction of specific antibodies capable of assisting the RES in the clearance and destruction of endotoxin. It is suggested that the present inconsistencies relative to the chemical nature and biological activities of endotoxins might be explained on the basis of these two activities and the failure to recognize the importance of the immunological state of the host in which the toxins are tested.

TOLERANCE OF DOG LUNG TO HYPERTHERMIC PERFUSION

Hyperthermia of the left lung of the dog was produced by pulmonary artery perfusion in 29 animals. It was found that the lung tolerates tissue temperatures up to 43 C for periods as long as 60 min without significant permanent disturbance of structure or function as measured by blood gas analysis, angiography, and contralateral pulmonary artery ligation. Elevation of the lung temperature above 43 C for periods longer than 10–12 min resulted in partial or total destruction of pulmonary tissue. Data are presented regarding perfusion techniques, factors affecting lung tolerance to hyperthermia, and possible areas for future study.

STUDIES ON THE PATHOGENESIS OF FEVER. 13. THE EFFECT OF PHAGOCYTOSIS ON THE RELEASE OF ENDOGENOUS PYROGEN BY POLYMORPHONUCLEAR LEUKOCYTES

1. Phagocytosis promotes the release of endogenous pyrogen from polymorphonuclear leucocytes. 2. The release of pyrogen, though initiated by the phagocytic event, is not synchronous with it. 3. The postphagocytic release mechanism is not inhibited by sodium fluoride and, therefore, appears not to require continued production of energy by the cell. 4. The release process, on the other hand, is inhibited by arsenite, suggesting the participation of one or more sulfhydryl-dependent enzymes in the over-all reaction. 5. Particle for particle, the ingestion of heat-killed rough pneumococci causes the release of approximately 100 times as much pyrogen as the ingestion of polystyrene beads of the same size. 6. The pyrogen release mechanism of polymorphonuclear leucocytes separated directly from blood, unlike that of granulocytes in acute inflammatory exudates, is not readily activated by incubation of the cells in K-free saline. Despite this difference, both blood and exudate leucocytes following phagocytosis release large amounts of pyrogen, even in the presence of K(+). The fact that the postphagocytic reaction is uninhibited by the concentrations of K(+) which are present in plasma and extracellular fluids, suggests that this mechanism of pyrogen release may well operate in vivo. 7. As might be expected from the foregoing observations, the intravenous injection of a sufficiently large number of heat-killed pneumococci causes fever in the intact host. Intravenously injected polystyrene beads, on the other hand, are significantly less pyrogenic. Evidence is presented to support the conclusion that the fever in both instances is caused by pyrogen released from the circulating leucocytes which have phagocyted the injected particles. 8. The possible relationships of these findings to the pathogenesis of fevers caused by acute bacterial infections are discussed.

STUDIES ON THE PATHOGENESIS OF FEVER. XII. ELECTROLYTIC FACTORYS INFLUENCING THE RELEASE OF ENDOGENOUS PYROGEN FROM POLYMORPHONUCLEAR LEUKOCYTES

The metabolic reactions responsible for the release of endogenous pyrogen from rabbit granulocytes incubated in 0.15 M NaCl are specifically inhibited by the presence of K⁺ (and by related alkali metal ions, Rb⁺ and Cs⁺) in the medium. The inhibitory action of K⁺ apparently involves penetration of the cell membrane and is directly antagonized by the cardiac glycoside, ouabain. It is concluded, therefore, that the inhibition of pyrogen release by extracellular K⁺ is due to transport of K⁺ into the cell. Although the precise molecular mechanisms which are responsible for the release of pyrogen from granulocytes incubated in K-free saline have not been elucidated, further study of the process has revealed: (a) that it is preceded by the accumulation of pyrogen within the cell, (b) that it depends upon the catalytic action of one or more sulfhydryl-containing enzymes, (c) that it does not require energy, either from glycolysis or from reactions depending on molecular oxygen, and (d) that its inhibition by K⁺ and by arsenite is qualitatively similar to the depression caused by these same reagents on the release of other leucocytic proteins; i.e., lysozyme and aldolase.

DIFFERENTIAL EFFECTS OF HEAT ON SPLENIC AND RENAL VASCULAR BEDS

The effects on vascular resistance of increasing blood temperature, from hypothermic to hyperthermic levels, were evaluated on denervated perfused spleens and kidneys in the dog. Temperature of the perfusate (blood) was increased for variable intervals of time from the hypothermic level of 32 C to the hyperthermic level of 42 C. The calculated resistance in the splenic vascular bed increased, whereas the resistance decreased in the renal vascular bed. It is concluded that heat has a differential effect in the splenic and renal vascular bed, causing vasoconstriction in the spleen and vasodilation in the kidney.